The present invention relates to magnetic flowmeters that employ magnets for determining the flow of electrically conductive liquids, such as liquid metals. Flowmeters of this type permit determination of flow within an unobstructed tube by establishing a magnetic field with lines perpendicular to the direction of the fluid flow. An electrical potential is generated across the flowing electrically conductive fluid that is a determinable function of the fluid velocity.
The tube or channel is of non-magnetic material to prevent interference with the magnetic lines passing through the flowing fluid. Suitable electrical pickup leads are provided on a diameter of the containment tube perpendicular both to the fluid flow and to the lines of the magnetic field. The movement of the electrically conductive fluid through the magnetic field cutting the lines of force develops an electrical potential that is a function of both the velocity of the fluid flow and the strength of the magnetic field. Through measurement of this electrical potential and knowledge of the field strength, the fluid flow can be determined in a calibrated magnetic flowmeter.
Prior magnetic flowmeters have required calibration due to variations in operating temperatures, in pipe wall resistivity and magnetic flux changes. The required calibrations to overcome these changed conditions can be inconvenient and cumbersome particularly when radioactive or hazardous liquids are employed. Such calibrations may be particularly inconvenient and undesirable in large scale processes involving large diameter flow channels.
The following patents and other publications are representative of the general field of the present development.
U.S. Pat. No. 3,967,500 to Forster discloses a magnetic flowmeter that includes first and second probes, one downstream of the other for detecting the A/C and D/C signal components generated by the flow of electrically conductive fluid through a magnetic field. Cross-correlation methods are employed to determine the time delay between the respective A/C signal portions and from that time delay the flow velocity within the flow channel.
U.S. Pat. No. 3,824,456 to Wiegand discloses a magnetic flowmeter in which a fluxgate element is employed to detect the magnetic field developed by the movement of fluid through a steady state magnetic field provided by permanent magnets. Various D/C balancing currents are coupled to the fluxgate to balance out undesired magnetic fields.
U.S. Pat. No. 3,736,798 to Wood et al discloses a probe type magnetic flowmeter for determining fluid flow by measurement of electrical potential developed in the flow of conductive fluid through a magnetic field.